1. Field of the Invention
The present invention relates to a molding die used to extrude a thin-walled honeycomb structure.
2. Description of the Related Art
A ceramic honeycomb structure, for example, one of the main components of which is cordierite, is manufactured by extruding materials using a molding die. The honeycomb structure comprises many cells formed by partition walls provided in a grid pattern, and the shape of the cell can be, for example, quadrangular and hexagonal.
As the above-mentioned honeycomb structure molding die, one is used that comprises supply holes through which materials are supplied and slit grooves that are communicated with the supply holes and mold the materials into the above-mentioned honeycomb shape.
Recently, the partition wall of the honeycomb structure has been required to be thinner, for example, not more than 150 xcexcm or 100 xcexcm. In accordance with this demand, naturally the groove width of the slit grooves of the honeycomb structure molding die is also required to be narrower.
If, however, the groove width of the slit grooves of the honeycomb structure molding die is narrowed, the flow of the materials, which are supplied through the supply holes, is obstructed when passing through the slit grooves. Therefore, the molding pressure during molding increases and the moldability may be degraded.
The present invention has been developed with these conventional problems being taken into account, and the object is to provide a honeycomb structure molding die that can mold a thin-walled honeycomb structure without degrading the moldability.
In the first aspect of the present invention, a honeycomb structure molding die is provided, which comprises at least supply holes to supply materials and slit grooves that are communicated with the supply holes and mold the materials into a honeycomb shape, wherein the groove width of the slit grooves is not more than 100 xcexcm and at the same time, a pair of opposing side surfaces of the slit grooves have recesses and protrusions extending in the direction in which the materials are extruded, respectively.
The honeycomb structure molding die of the present invention has, as described above, very narrow slit grooves, the groove width of which is not more than 100 xcexcm. Therefore, when the honeycomb structure molding die is used for extrusion, the flowability of the materials is degraded and concern over the increase of the extrusion pressure may arise.
In the present invention, the recesses and protrusions are provided on the side surface of the slit grooves, as described above. They extend in the direction in which materials are extruded during extrusion. Therefore, when the materials flow, the recesses and protrusions play a role in guiding the materials to flow in a desired direction. In this manner, the flowability of the materials during extrusion can be improved, the fluidity of the materials can be maintained high and the increase of the molding pressure can be suppressed even when the groove width of the slit grooves is as narrow as 100 xcexcm or less.
As a result, according to the honeycomb structure molding die of the present invention, a thin-walled honeycomb structure can be molded without degrading the moldability.
In the second aspect of the present invention, a honeycomb structure molding die is provided, which comprises at least supply holes to supply materials and slit grooves that are communicated with the supply holes and mold the materials into a honeycomb shape, wherein the groove width of the slit grooves is not more than 100 xcexcm and, at the same time, the pitch P1 of the protrusions, which is obtained by measuring the surface roughness in the direction in which the materials are extruded, and the pitch P2 of the protrusions, which is obtained by measuring the surface roughness in the direction perpendicular to that in which the materials are extruded, satisfy the relationship P1/P2 greater than 1.5, on a pair of opposing side surfaces of the slit grooves.
In the present invention, the surface roughness of the side surface of the slit grooves in the direction in which the materials are extruded differs from that in the perpendicular direction, as described above. In addition, the pitch P1 of protrusions in the direction in which the materials are extruded and the pitch P2 of protrusions in the perpendicular direction satisfy the relationship P1/P2 greater than 1.5, that is, the pitch P2 is longer than the pitch P1, as described above.
Having such surface roughness enables the side surfaces of the slit grooves to maintain a state in which proper recesses and protrusions are formed in the direction in which the materials are extruded. Therefore, the surface roughness of the side surfaces plays a role in guiding the flow of the materials when the molding materials are extruded.
In this manner, the flowability of the materials during extrusion can be improved, therefore, the fluidity of the materials can be maintained high and an increase in the molding pressure can be suppressed even when the groove width of the slit grooves is as narrow as 100 xcexcm or less.
As a result, according to the honeycomb structure molding die of the present invention also, a thin-walled honeycomb structure can be molded without degrading the moldability.
It is preferable, in the present invention, that the pitch of the recesses is 180 xcexcm to 200 xcexcm. If the pitch of the recesses (pitch of the protrusions) is less than 150 xcexcm or the pitch of the recesses exceeds 220 xcexcm, a problem that the effect to guide the materials to flow in a desired direction is decreased is caused, in each case.
It is also preferable that the depth of the recesses or the height of the protrusions is 6 xcexcm to 12 xcexcm. If the depth of the recesses or the height of the protrusions is less than 4 xcexcm, the effect to guide the materials that pass through the slit grooves to flow in a desired direction is excessively decreased. On the other hand, if it exceeds 14 xcexcm, the effect to guide the materials to flow in a desired direction is excessively increased and there appears a possibility that most of the materials may only pass through a limited area.
On the other hand, it is preferable that not less than 50% of the protrusions on one side of the opposing side surfaces oppose the protrusions on the other side thereof. Thus, the effect to guide the materials to flow in a desired direction can be fully realized. When less than 50%, the effect due to the construction in which the protrusions on one side surface oppose those on the other side surface cannot be properly achieved.
It is also preferable that the recesses and the protrusions are constructed by randomly arranging unit recesses and unit protrusions, the dimensions of which are shorter than the groove depth of the slit grooves. In this case, the materials can easily shift transversely from the unit recess or the unit protrusion to the next unit recess or the unit protrusion when the materials are moved in the extruding direction, and the pressure increase in the transverse direction by flow obstruction can be easily prevented.
It is preferable here that the length of the unit recess and the unit protrusion is 13 xcexcm to 18 xcexcm. If the length is within this range, it is possible to form them by using a laser machining method, which will be described later, and adjusting the pulse width of the laser beam.
In addition, it is possible to set the groove depth of the slit grooves to not less than ten times the groove width. In this case, the slope of the angular portion works effectively to prevent the obstruction of the flow of the molding materials.
The present invention may be more fully understood from the description of the preferred embodiments of the invention set forth below, together with the accompanying drawings.